Selective laser melting of a high-strength aluminium alloy

Additive manufacturing (AM) of highly complex three-dimensional metal structures using selective laser melting (SLM) is increasingly gaining interest in numerous fields of application. The new design freedom combined with enhanced lightweight design methods shows an enormous potential, especially in the aerospace industry. Thereby, metal alloys with a high strength to weight ratio play an important role. Although several titanium and aluminium alloys have been SLM-processed successfully, the high strength-aluminium alloy EN AW 7075 remains a challenge. The major challenge in SLM processing of EN AW 7075 is the high sensitivity to hot cracks due to process related temperature gradients and rapid solidification. Preheating represents a promising approach to reduce temperature gradients and minimize shrinking between the layers. This investigation focuses on optimum SLM process parameters and reduction of hot cracking of EN AW 7075. In the first step, hot crack formation was evaluated from single track experiments to identify the most promising range of laser parameters. Subsequently, multi-layer parameter studies were carried using EN AW 7075 powder and preheating of up to 350 °C

Laser powder bed fusion of 30CrNiMo8 steel for quenching and tempering : examination of the processability and mechanical properties

The layer-by-layer principle of additive manufacturing technology laser powder bed fusion (LPBF) opens up completely new possibilities in the design and manufacturing of lightweight and efficient gear components. For example, integration of contour conform cooling and lubrication channels into gear components can increase their service life and reduce lubricant consumption. Steels for quenching and tempering and case hardening steels are commonly used materials for gear components. However, the availability of these alloys for LPBF processing is still limited. In particular, the 30CrNiMo8 steel for quenching and tempering is frequently used for gear wheels. This specific alloy is largely unknown regarding LPBF processing and remains challenging, because of its susceptibility to cracking and the high temperature gradients that occur during the LPBF process. Therefore, this study focuses on the LPBF processing of 30CrNiMo8 powder material including process parameter evaluation and material characterization. Additionally, effects of the heat treatment on the resulting microstructure and mechanical properties were investigated. Within this study the 30CrNiMo8 has been processed successfully with a density of well above 99.5% leading to promising mechanical properties. A more homogenous microstructure has been achieved with quenching and tempering, compared to the as-build state

Dynamic conformal cooling improves injection molding : hybrid molds manufactured by laser powder bed fusion

To achieve a certain visual quality or acceptable surface appearance in injection-molded components, a higher mold Surface temperature is needed. In order to achieve this, injection molds can be dynamically tempered by integrating an active heating and cooling process inside the mold halves. This heating and cooling of the mold halves becomes more efficient when the temperature change occurs closer to the mold surface. Complex channels that carry cold or hot liquids can be manufactured close to the mold surface by using the layer by layer principle of additive manufacturing. Laser powder bed fusion (L-PBF), as an additive manufacturing process, has special advantages; in particular, so-called hybrid tools can be manufactured. For example, complex tool inserts with conformal cooling channels can be additively built on simple, machined baseplates. This paper outlines the thermal simulation carried out to optimize the injection molding process by use of dynamic conformal cooling. Based on the results of this simulation, a mold with conformal cooling channels was designed and Additively manufactured in maraging steel (1.2709) and then experimentally tested

Increasing the safety against scuffing of additive manufactured gear wheels by internal cooling channels

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)The layer-by-layer principle of the additive manufacturing (AM) technology of Laser-Powder-Bed-Fusion (LPBF) creates new opportunities in the design and manufacturing of efficient gear components. For example, integrating a cooling system can increase the safety against scuffing or reduce the amount of required lubrication and thus the splashing losses. Quenched and tempered steels or case-hardened steels are commonly used in the fabrication of gear components. However, the availability of these alloys for LPBF processing is still limited. The development of suitable LPBF metal gears (with a Gear Research Centre (FZG) type A geometry) out of quenched and tempered 30CrNiMo8 steel with internal cooling channels shows the possibility of significantly increasing the safety factor against scuffing. This work includes the development of a suitable cooling strategy, material development, the setup of a suitable test infrastructure and the analysis of the LPBF gears tested for scuffing

Properties of additive-manufactured open porous titanium structures for patient-specific load-bearing implants

Additive manufacturing has been well established in many sectors, including the medical industry. For load-bearing bone implants, titanium and its alloys, such as Ti6Al4V, are widely used due to their high strength to weight ratio and osseointegrative properties. However, bone resorption and loosening of implants is related to the significantly higher stiffness of dense Ti6Al4V, leading to stress shielding. With the aging of population, there is an increasing need for orthopedic implants with a high success rate and a long implant life span. Besides that the treatment of non-healing segmental bone defects, where the self repairing properties of bone tissue are not sufficient, is still a challenge. In both fields of application, patient-specific titanium implants combined with functionally graded porosity designed according to locally expected loads unlock new possibilities. Many studies underline the huge potential of the new design freedom to generate open porous structures and more personalized implants with enhanced mechanical properties that also integrate well with surrounding tissues. Integration of functionally graded open porosity into implants allows for the implant to more closely mimic the mechanical properties of human bone and its internal architecture. The results of this work represent the basis for developing complex porous titanium structures with various pore sizes and shapes to tailor structural mechanical properties and biological responses. Therefore, 3D porous structures with various pore sizes and shapes were designed and manufactured in Ti6Al4V using laser powder bed fusion (PBF-LB/M). Based on these structures, the correlation of pore size and shape with cell ingrowth, morphology, metabolic activity, and early markers for bone formation (ALP activity) was investigated in static cell cultures using the osteosarcoma cell line Saos-2. Mechanical properties, such as stiffness and compression strength, were investigated with compression testing. The present study concludes that cell morphology, metabolic activity, and ALP activity are widely independent of pore shape and size within the tested range of 400–700 µm pore size. Furthermore, the mechanical properties of the evaluated structures were in the range of cortical and trabecular bone. This opens the possibility to design mechanical properties with gradient porosity without decisively affecting biological responses

Mit additiver Fertigung zu innovativen Getriebekomponenten

Kleinere Massenträgheitsmomente und optimierte Gestaltung für Kühlung, Schmierung und Zahneingriff können die Effizienz von Getriebe merklich erhöhen. Im LPBF-Verfahren additiv hergestellte Zahnradkomponenten mit typischen Getriebestählen wie beispielsweise dem 30CrNiMo8 bieten dabei grosses Potenzial. Der Vortrag zeigt, wie das Wissen im Bereich Zahnrad- und Getriebedesign und des PLBF-Verfahrens erfolgreich kombiniert werden